When working with many layers, many filters and folders and in 16bit colors, i have now experienced twice in two different circumstances where Photoshop fails to deliver a layer merge or even just spit out the image as a regular jpeg without causing this glitch effect. I spend hours locating (not 100%) what the problem is about.

I believe there's something with adding a FX shadow with added noise to it.

When this is put inside a folder, and then has a clipping mask to it. Things can get nasty.

Again i can't 100% replicate it, but i've managed to do it in my two latest projects with the latest version of Photoshop CC 2018.

I hope this will be fixed very soon as this hinters me greatly and causing me to lose precious time searching for the problem and unticking that one "thing".

I also recorded my monitor so you can see what is going on. The glitch is random from every merge of layers.